The invention pertains to a method for steering a ground-drilling machine, in particular, a drill column assembly with a drilling head which is driven in the ground in rotative, propulsive and, if so required, percussive fashion.
In one known method for steering a drilling machine, the drilling head has a beveled surface that causes a deflection of the machine if the rotation of the drilling head is interrupted.
In order to determine the position of the drilling head in the ground, a transmitter that, for example, is supplied with energy via batteries is arranged in the drilling head. This transmitter comprises measuring devices that make it possible to measure the depth of the drilling head, the position of the drilling head in the ground as well as the incline and the roll-off of the drilling head relative to its axis, i.e., the angular position of the beveled surface relative to the longitudinal axis. In addition, it is also possible to determine the temperature of the drilling head.
The measured data is transmitted from the transmitter arranged in the drilling head to a receiver on the surface and displayed at this location. Subsequently, the data is transmitted in wireless fashion to the operator of the rotation and propulsion unit and also displayed at this location. This data makes it possible to initiate a steering maneuver, e.g., by interrupting the rotation of the pipe string assembly in a certain angular position of the beveled surface which corresponds to the position, in which the deflection should take place. In this position, the pipe string assembly with the drilling head is only driven in translational (propulsive or percussive) fashion such that the beveled surface generates a lateral force that causes a steering movement.
FIG. 1 shows how a conventional steering maneuver is carried out if the pipe string assembly should extend along a road curve that, for example, has a curvature radius of 60 m. A straight hole 1 should continue at a predetermined radius of curvature beginning at a point 2. The rotation of the pipe string assembly is interrupted by a control signal in position 2 such that the drilling head is deflected in the desired direction over a section 3. However, this deflection corresponds to the maximum deflection that can be attained with the beveled surface of the drilling head, i.e., the rotation of the pipe string assembly must be resumed via a control signal in position 4 so as to realize the ensuing linear section 1. The rotation of the pipe string assembly or the drilling head, respectively, neutralizes the effect of the beveled surface of the drilling head. Consequently, it is necessary to interrupt the rotation of the pipe string assembly anew and initiate another deflection of the pipe string assembly after a certain distance.
Due to this phased interruption of the pipe string assembly, the hole in the ground extends in zigzag fashion, i.e., the pipe string assembly is subjected to intense stresses because it must follow this zigzag-shaped progression. In addition, it is possible for the drilling head to become jammed in the ground during longer steering movements, i.e., while the pipe string assembly does not rotate. This means that the pipe string assembly can resume its rotation after the steering movement is completed only if the torque is increased, i.e., the pipe string assembly is subjected to very high peak stresses.
This situation remains the same if dynamic percussions generated by a percussion unit are exerted upon the pipe string assembly in addition to the static propulsion generated by the rotation and propulsion unit. This percussion unit which, for example, acts upon the drilling head via the pipe string assembly or is directly arranged on the drilling head, makes it possible to carry out steering movements during the advance of the drilling head in hard, dense soils.
In order to improve the earth-removal effect of the drilling head, it is conventional to supply a fluid, in particular, a bentonite suspension, to the drilling head via a tubular pipe string assembly. This fluid is discharged from nozzles on the drilling head in the form of a cutting jet that serves for loosening the soil and/or improving the removal of the loosened soil as well as cooling the drilling head and the locating and transmission device.
Instead of transmitting the measured data from the transmitter to a receiver on the surface in wireless fashion and forwarding said data from this receiver to the operator of the rotation and propulsion unit, it is also conventional to transmit the data from the measuring system in the drilling head that may also contain the energy supply for the measuring system to the rotation and propulsion unit via a cable that extends through the pipe string assembly and display the measured data at this location. This technique of transmitting the data by means of a cable is utilized particularly in instances in which it is not possible to walk on the surface within the region of the hole.